/**
 * jQuery滚动加载插件scrollLoading，将其封装做成插件
 */
(function($) {
    $.fn.scrollLoading = function(options) {
        var defaults = {
            attr: "data-url"    
        };
        var params = $.extend({}, defaults, options || {});
        params.cache = [];
        $(this).each(function() {
            var node = this.nodeName.toLowerCase(), url = $(this).attr(params["attr"]);
            if (!url) { return; }
            //重组
            var data = {
                obj: $(this),
                tag: node,
                url: url
            };
            params.cache.push(data);
        });
        
       //动态显示数据
        var loading = function() {
            var st = $(window).scrollTop(), sth = st + $(window).height();
            $.each(params.cache, function(i, data) {
                var o = data.obj, tag = data.tag, url = data.url;
                if (o) {
                    post = o.offset().top; posb = post + o.height();
                    if ((post > st && post < sth) || (posb > st && posb < sth)) {
                        //在浏览器窗口内
                        if (tag === "img") {
                            //图片，改变src
                            o.attr("src", url);    
                        } else {
                            o.load(url);
                        }    
                        data.obj = null;        
                    }
                }
            });        
            return false;    
        };
        
       //事件触发
        //加载完毕即执行
        loading();
       //滚动执行
        $(window).bind("scroll", loading);
    };
})(jQuery);